The present invention is directed to various improvements in a float and valve assembly for a liquid-gas accumulator. The improvements include a buoyant float which is connected to the valve in which the float has a density selected in accordance with the working pressure, and in which the float can be lengthened or shortened in responses to the type of liquid used and the altitude of use. In order to reduce friction and drag as the valve is longitudinally actuated, the ratio of bore length to valve rod length has been optimized, a crown is provided to reduce spring variance from the perpendicular, the valve stem and bore is honed to reduce drag, and grooves are provided in the periphery of the valve stem to reduce friction.
It is known as described in U.S. Pat. Nos. 5,097,862 and 5,520,208 to provide a liquid-gas accumulator having a buoyant float connected to the inlet-outlet valve for avoiding the problems encountered by various guided float-type accumulators, which have been used in the past, which are subject to the possibility of cocking or sticking and malfunctioning.
Liquid-gas accumulators have had various applications, such as in the oil and gas drilling industry, and typically have a working pressure of 3000 psi and are limited to an underwater working depth of 7000 feet. However, there is now a need for accumulators having a greater working pressure of 6000 to even 10,000 psi and an underwater working depth of 17,000 feet. The prior art float structures did not foresee the problems involved in using different pressures. It would generally assume that the prior art designs would work at any pressure. However, field use shows that at pressures above 3000 psi, the float material of the prior art could crush or absorb working fluid. An improved float was needed at higher pressures.
In addition, prior art float-type accumulators were designed with the assumption that water was used as the working fluid at sea level. Water has a specific gravity of 1.00 at sea level. The prior art accumulators work because of the differential between the specific gravity of the water and the lower specific gravity of the float material. The differential is commonly known as buoyancy. However, field use demands a multitude of fluid compatibilities and of altitudes. Alternate fluids have a different specific of gravity, so consequently the buoyancy changes, and the float and valve assembly is no longer balanced. Altitude also affects the buoyancy in a similar fashion. The total buoyancy of the float is its specific gravity times its mass in ratio to the accumulator fluid""s specific gravity at the altitude selected. Therefore, the mass of the float must be adjusted to solve these problems.
Yet another problem in the prior art float mechanisms is the issue of friction and drag. In order to work effectively, the float and valve assembly must travel up and down vertically. While the float and valve assembly of the present invention avoids the use of guided cages which have inherent friction and drag, variance from perpendicular of the present float and valve assembly reduces the efficiency of the operation. The float valve assembly tends to be top heavy and any wobble between the valve stem and its supporting bore causes drag and friction, therefore, a need for maintaining vertical alignment of the valve and float assembly is desired.
Yet another problem is that the opening biasing spring in the prior art accumulator acts against the bottom of a poppet valve causing the valve to lean to one side and thus adding to the variance from perpendicular. Therefore, in order to hold the spring in the vertical position, there is a need to direct the force of the spring upwardly.
Another field problem noted is that the float and valve assembly must travel up and down smoothly and any drag or friction between the valve stem and its supporting bore adds to the inaccuracy of operation.
Various improvements are provided for aligning the valve in a vertical direction for longitudinal movement by better and smoother contact support between the valve stem and supporting bore. However, fluid which is trapped between the valve stem and bore creates a negative force impeding the smooth operation and a need is desired to reduce fluid drag.
One feature of the present invention is the provision of a float and valve assembly for a liquid gas accumulator in which the density of the float is selected so that it can be matched to the anticipated working pressure. In one preferred embodiment the density of the float is selected to be greater than 44 pounds per cubic feet to thereby accommodate higher pressures.
Another improvement of the present invention is wherein the mass of the float is adjusted in order to allow the accumulator to properly work with a higher or lower specific gravity fluid or at a higher or lower altitude. In the preferred embodiment a float having a plurality of segments can be used to be lengthened or shortened to meet the operating conditions for different fluids and different altitudes.
Another improvement of the float and valve assembly is to lengthen the supporting bore around the stem of the valve to reduce wobble and insure that the float and valve have less variance from the perpendicular. In the preferred embodiment the preferable length of the bore relative to the length of the float and valve assembly is 1:5.05.
Another improvement to the present invention is a provision of a crown on the underside of the poppet valve to engage and hold the spring in a vertical position to prevent the spring from pushing the valve out of its vertical alignment.
Still a further improvement to the present invention is the provision of honed surface finishes on the coacting surfaces of the bore support and the poppet valve stem for reducing drag.
And still a further improvement is the provision of one or more grooves cut on the outer periphery of the valve stem to channel fluid therein to reduce the drag of the valve stem in its supporting bore. In the preferred embodiment the grooves are longitudinally and axially positioned on the stem.
Still a further object of the present invention is the provision of a float and valve assembly for a liquid-gas accumulator having a housing with a top gas port and a bottom liquid port, a gas charging valve positioned in the top port for admission of high pressure gas, and a sleeve releasably connected in the liquid port and including a valve seat. The float and valve assembly includes a vertically extending bore in the sleeve, a poppet valve element coacting with the seat for opening and closing the port and including a stem longitudinally movable in the bore, spring means positioned between the sleeve and the bottom of the poppet valve element yieldably urging the valve to the open position, and a buoyant float rigidly connected only to the poppet valve element for controlling the opening and closing of the valve in response to the level of liquid in the housing. The float has a density selected to be sufficient to avoid failure at the desired working pressure. In a further embodiment, the density of the float is greater than 44 pounds per cubic feet.
Still a further object is wherein the float includes a plurality of segments whereby the buoyancy of the float may be changed to meet operating requirements.
Still a further object is wherein a crown is provided on the bottom of the poppet valve coacting with the top of the spring to maintain the spring in the vertical position.
Yet a still further object is wherein the stem includes an outside coacting with an inside of the bore and wherein the outside and inside are honed to a finish for reducing friction and drag. In the preferred embodiment the finish is a maximum of 16 on a mirror finish gauge.
Yet a still further object of the present invention is wherein the ratio of the length of the bore relative to the length of the float and valve assembly is 1:5.05.
Still a further object is wherein the stem includes an outside having one or more grooves cut in the outside for reducing drag between the stem and the bore. In one embodiment the grooves are axially extending.
Other and further objects, features and advantages will be apparent from the following description of a presently preferred embodiment of the invention, given for the purpose of disclosure, and taken in conjunction with the accompanying drawings.